Extending the range of wireless weather stations with walkie talkies

[Roel] wanted to put a wireless weather station in his greenhouse. Even though the weather station was supposed to transmit over fairly long distances, the geometry of his back yard and a few stone walls killed the radio signal even after putting a good antenna on the receiving side of his wireless weather station setup. Wanting to get his weather station working, [Roel] did the sensible thing and built a packet radio setup out of a pair of walkie talkies, greatly increasing the range of his weather station.

This build comes after [Roel] spent a great deal of time reverse engineering the wireless protocol of his Thierry Mugler weather station. With a little bit of code, [Roel] is able to get the current temperature and humidity reading into his Linux box. This system relies on the transmitter inside the weather station, so the system falls apart over any sufficiently large distance.

To increase the range of his weather station, [Roel] took his existing hardware and added a pair of inexpensive FRS walkie talkies. The build uses the hardware from his previous build to get the radio data from the weather station. This data is sent over to an ATmega88 where it’s converted to packet radio and sent over the walkie-talkie. On the receiving side, the output of a second walkie-talkie is piped into the Linux soundmodem app (link, but it’s down as of this writing) where it’s decoded. Sending the received data to gnuplot makes a very nice graph of the temperature and humidity.

[Roel] put the code for both the tx and rx sides of the build up on his build page. Very nice work that uses very inexpensive hardware.

I don’t think we really should care whether or not he’s using an frs radio. A lot of hacks aren’t always legal or nice. But at least they are cool and could help in a national emergency. This is hackaday. Not politically-correct-device-re-purposing-a-day.

So if during this “national emergency” you were trying to communicate with your family over an frs radio, and all you could pick up was digital chirping because this guy was taking over the channel with his hack, then you might not be so happy. Something to think about.

Concerning the illegality of transmitting data over civilian voice channels:
Would it still be considered illegal if you used Text to Speech (TTS) software to send your desired information via the walkie talkies?

thats a bit of a grey area but it would never hold up in court so long as the speech is satanical
tho side note this appears as a much MUCH less cost effective method
not just the radios but also the resulting FCC lawsuit :P

And honestly who cares… anyone who needs reliable radio comm’s wont be using PRM446 with its pitiful 0.5W limit only ppl who use this for actual comms are 12 year old’s with there Argos bought PRM446’s…. A proper UHF licence is literally pennies and allows up-to 5W

Thanks hack a day, for featuring it, and thanks hackers, for your comments!

Regarding the legalities, I have no idea, I have to admit. Here in the Netherlands, there used to be a huge packet radio network over the entire country back in the 90s, but it used 27MC radios. Whether it is legal or not, I doubt that my system will cause any harm. I send a frame every 10 minutes, which is about one second long. So I occupy one of the eight PMR446 channels for 0.167% of the time. I could live with that, morally.

And yes, I tried connecting a directional antenna (Yagi-Uda) aimed at the sensor, but that was not sufficient. I didn’t try directional antennas on both sides though. I admit my way to solve this “problem” is a bit crazy, but my approach has way more uses beyond wireless weather stations. It can be re-used for APRS for example, and there are countless other uses for a cheap wireless few-km/mile link at 1200bps.

Oh, and a minor note: I didn’t use that soundmodem app, I wrote a limited replacement for it, as I couldn’t manage to make it work. And writing an AFSK demodulator was more satisfying than reusing one of course ;)

Well if you are worried about the FCC then just use the 27 MHZ CB band. The FCC gave up any enforcement of those frequencies about 40 years ago unless you run more than about 5000 watts and slop your signal all over the spectrum. Realistically, unless you make a real nuisance of yourself, the chances of the FCC bothering you is about equal to the chances of a powerball win. I have a friend who has monitored water levels at a remote stock tank using FRS for about 10 years now. It starts beeping when when the water is low. A beep every minute is barely noticeable if if somebody was using the freq legitimately. And he uses that freq for his voice operations and has never heard anyone else on there. It is in a real rural area (BFE) and down a valley so there is really no possibility of a problem.

FCC has nothing to do with this as it is in europe.
And around here it is legal to use data modes on PMR446.
It is not in the spirit of the service, but it was never specialy forbidden so it is ok to do so.
People have done stuff like SSTV experiments.

But adding antennas is illegal and against regulations everywhere.
Even inductively coupled one’s are illegal here, so no reflectors either.

I was not nitpicking, just making sure people understood that. There’s so much people running modded 5w UHF handies these days that none gives a crap about power on PMR446. Same with antennas.
Some wierd people run 50w (100x the legal maximum) to directional antennas here.
At that point they might as well get a hamradio lisence and run something like a kW on 433MHz :)

On the subject of 433MHz, that weather station uses standard ISM band 433MHz modules, you could easily add antennas to it legaly. And illegaly you could add a power amplifier.
Like a mitsubishi module (little drive goes in, 16W+ comes out). All the ham 70cm stuff works 1:1 here as the device actualy operates inside the hamband.

try connecting the tx and rx anntennas DIRECTLY with a VERY long wire?

works to extend the range of many things, albiet non-wirelessly. but at least its one wire instead of like how many if not RF? minimum two. and probably jumps the gap where the twisted together wires corroded in the rain :)

BUT… props for reverse engineering the protocal, i’d have done the same if i had the patience.

unfortunately i only have the patience of ripping out the uC in the tx and building from scratch using bare sensors (hacked not purchased) and the 433tx (hacked not purchased) combined with my own uC (purchased OR hacked)

As for the OP, this is the best description of how the amateur radio AFSK modulation is set up. I recently implemented a modulator myself and it was a real headache to figure this out by trial and error with no good documentation anywhere. Ditto AX.25, though that is somewhat more clear than the modulation.

My modulator uses the PWM and a low pass to produce a reasonable sine that is relatively well balanced. Some demodulators can have difficulty with signals that have a lot of ‘twist’.

Working on an APRS tracker design I might try to release commercially, but for now just testing.